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Remote SSR feeds for airport approach control

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Remote SSR feeds for airport approach control

Old 3rd Nov 2019, 21:38
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Remote SSR feeds for airport approach control

At airports which don't have their own SSR head but buy in coverage from a remote site or sites, would it be possible and/or desirable for the radar display to simultaneously show data from more than one site ? For example, Leeds Bradford Airport has, for many years, used the NATS site at Claxby as its preferred SSR provider, with Great Dun Fell as a back up. Would it be technically or theoretically possible for both to be used at once to provide improved overall coverage ? There could well be a cost implication but I wondered if multiple site coverage would otherwise be advantageous.

Thankyou.
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Old 4th Nov 2019, 17:15
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If you’re buying a service, you may simply specify the service your want and the performance you are contracting to ....how your service provider provides it may be immaterial so long as you can rely on it for the performance you specify, and in turn the services you use it to provide.
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Old 4th Nov 2019, 17:28
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I think it's done in France but the CAA frown on it.
It should be possible by feeding different SSR plots into a computer and choosing the 'best' one but this will not necessarily show the SSR plot in a position accurate enough for use in vectoring aircraft in an instrument pattern and could show extensive track jitter.
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Old 4th Nov 2019, 19:35
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Thankyou both. I honestly didnt know the practical or technical ins and outs of what I was thinking. However, from the point of view of LBA, Great Dun Fell could provide improved SSR coverage in the high ground to the north and west of the airport, whereas Claxby would be better suited to cover areas to the south of LBA. That said, there are several ATC radar units in said area (Doncaster, Humberside, East Midlands and Manchester) already.
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Old 4th Nov 2019, 23:27
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Depends on the software that your radar data is fed into. Many places have multiple radar feeds to one display to cater for terrain issues. Have 3 feeds where I work. To merge the feeds, the display is chopped up into small squares. Each square has a percentage bias for each radar and displays the composite result. As aircraft close to each other are processed using the same or similar bias, any error applies equally to both aircraft.
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Old 5th Nov 2019, 07:25
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Originally Posted by Mooncrest View Post
Thankyou both. I honestly didnt know the practical or technical ins and outs of what I was thinking. However, from the point of view of LBA, Great Dun Fell could provide improved SSR coverage in the high ground to the north and west of the airport, whereas Claxby would be better suited to cover areas to the south of LBA. That said, there are several ATC radar units in said area (Doncaster, Humberside, East Midlands and Manchester) already.
I don't think any of those 4 airfields have their own interrogator apart from perhaps Manchester.
At Farnborough, each of the 3 LARS sectors has 2 radar displays and can potentially access 5 different radar feeds one at a time both primary and secondary. We wanted to 'mosaic' different feeds onto the same display but for various reasons, the CAA would not approve it.
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Old 5th Nov 2019, 21:24
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It will be interesting to see what equipment LBA selects when the time finally comes to replace the Watchman primary. The processing equipment was upgraded about three years ago with 4G-proofing done before that so this may not be any time soon. The Watchman has proved to have considerable longevity at LBA - been in service for just shy of thirty years and has long outlived its ACR430 predecessor. I wonder if LBA will this time buy their own SSR aerial or continue the supply arrangement with NATS.
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Old 5th Nov 2019, 22:37
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There are a number of problems that can arise if there are too many SSR interrogators within the same area. In Europe/EU there are rules which effectively limit the number of SSR interrogators to the minimum number necessary to provide the coverage required. This means, in practise, that data must be shared. If you really can't sleep at night, take a look at Commission regulation 262/2009.

There are some situations where having a transponder signal is very useful but was not intended or widely foreseen when SSR was developed. A good example is the use of transponders to track movement of aircraft and vehicle on the surface of an airport. In part to overcome problems with too many interrogators when one wants to monitor ground movements a new mode of operation was introduced to supplement mode S operations by which in certain circumstances transponders can send a 'reply' without being interrogated, this is commonly known as squitter. Mode S squitter transmissions are also used by ACAS/TCAS, again in part to avoid having multiple interrogators. (Squitter is, in fact, a generic term related to radio signals which follow the structure of a response in a cooperative nav/data system but are unsolicited.)

If such things interest you and you haven't already found it, there's lots of stuff out there which can be Googled.

Last edited by LookingForAJob; 6th Nov 2019 at 15:27.
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Old 6th Nov 2019, 08:09
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Thankyou, Looking, that's an interesting angle. I'm sure I've read before about how multiple SSR interrogators can create problems. I guess in the UK, either the CAA or OFCOM get to decide which units can have their own SSR and which can't. Using the system to track ground movements would be advantageous for LBA, given its infamous weather and current lack of ASMI.
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Old 6th Nov 2019, 16:12
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Sorry, missed out a 'not' in my previous mail - fixed it now.

Multilateration (MLAT) is probably the leading technology for surveillance of an airport surface activity. Typically, I think, the systems utilise transponder squitter but can also interrogate transponders if an update is required (for increased accuracy, for example). Not sure how the MLAT interrogators fit in with the EU regulation I mentioned previously (I'm sleeping quite well at the moment) but I presume they use much the same electronics and signal structure as used for 'classic' SSR.
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Old 6th Nov 2019, 17:59
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The RAF have interrrogators at some airfields in addition ot those operated by NATS.
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